1. Field of the Invention
The invention relates to voltage generation systems in general and, more particularly, to high voltage converters for converting logic level voltage signals to high voltages necessary for writing and/or erasing semi-conductor circuit devices such as E2PROM, etc.
2. Prior Art
The use of non-volatile memory systems has increased over the past few years. A typical non-volatile memory system includes a power generating system and a non-volatile memory system. The power generating system is usually integrated with the non-volatile memory system on a single chip. The non-volatile memory system is an array of floating gate memory cells which are written into and/or read by high voltage signals. The high voltage signals are generated by the power generating system.
The prior art provides several different types of power systems for driving non-volatile memory cells. Some of the prior art power systems are well suited for use with high voltage technology while others are suited for use with low voltage technology. In a high voltage technology, the power system devices can withstand relatively high voltage level signals without breaking down. This implies that the power supply system can be loosely controlled. However, in a low voltage technology the power system devices are sensitive to relatively high voltage and care must be taken to avoid breakdown of the devices. Because of the tight control which is designed into the power supply of the present invention, it allows low voltage technology devices to be used to generate high voltage.
Examples of prior art power supplies suitable for use with high voltage technology include U.S. Pat. Nos. 4,506,350; 4,404,475; 4,393,481; 4,186,436; 4,302,804; 4,368,524 and 4,263,664.
U.S. Pat. No. 4,506,350 provides a non-volatile semi-conductor memory system with a boosting circuit for boosting a write voltage applied to the memory system. The boosting circuit includes an oscillator which accepts a stable write voltage of 5 volts and boosts it to a higher level.
U.S. Pat. No. 4,404,475 described a voltage generating circuit wherein an unregulated charge pump provides a high voltage pulse which is trimmed by a regulator circuit to provide a satisfactory voltage for driving a non-volatile memory integrated circuit.
U.S. Pat. No. 4,393,481 describes an on-chip high voltage generator having a charge pump and a capacitive sensing output circuit. A gated diode is used to set the maximum output voltage of the charge pump.
U.S. Pat. No. 4,186,436 describes an uncontrolled voltage generator which uses stacked capacitors to provide a high voltage.
U.S. Pat. No. 4,302,804 describes an unrelated d.c. voltage multiplier in which a four position sequential counter drives a charge pump composed of diodes and capacitors.
U.S. Pat. No. 4,368,524 describes a voltage generating circuit for an E2PROM. The generating circuit includes a charge pump which receives an externally generated +5 and +20 volts and boosts them to a desired operating level.
U.S. Pat. No. 4,263,664 described a voltage generating circuit with a charge pump which is controlled by a gated breakdown diode.
A voltage generating circuit which can be integrated with an electrically alterable high density semi-conductor memory is described in U.S. Pat. No. 4,481,566. The circuit is best suited for use in a low voltage technology. It includes a capacitive charge pump with a single feedback loop including a DETS (Dual Electron Injector Structure) device for controlling the charge pump. Processing techniques are used to enhance the voltage characteristics of the devices beyond normal technology breakdown limits.